Resistance Prediction for Streams under Low Flow Conditions

Flow resistance under low flow conditions has been studied by many researchers because of its importance in practical applications, and different modifications of resistance coefficients such as Manning's n, Chezy C and the Darcy-Weisbach f for application under appropriate conditions have been proposed. The strong variation of these coefficients with flow depth suggests that the form of these equa- tions is not appropriate for shallow flows. An alternative equation form for resistance prediction under low flow conditions is proposed. It distinguishes between the influences of large-scale and intermediate- scale roughness on flow resistance by a coefficient that depends on the relative submergence. The equa- tions performance is confirmed by comparison of predicted and measured velocities using published ex- perimental and field data.